The present invention relates to a color image reader for reading two-color images by decomposing them into independent color components.
Some modern facsimile apparatuses have a capability for transmitting a document in which, for example, particular information to be stressed is written or underlined in red. Various types of color image readers have been proposed and put to practical use for implementing such a capability, i.e. reading two-color information. The prior art color image readers which are capable of reading red information as well, for example, may generally be classified into two types, i.e. a light source sequential type and a filter separation type. The light sequential type image reader is such that two light sources, one emitting white light and the other red light, illuminate a document so that reflections from the document are read by line image sensors. The filter separation type, on the other hand, is such that a light source emitting white light illuminates a document to cause the reflection to be focused by an imaging device and, while a dichroic mirror, a dichroic prism or the like separates the focused light into a red component and the other, line image sensors read the color components.
The problem with the light source sequential scheme is that since the positions to be illuminated by the two light sources are remote from each other, intricate processing is necessary for output signals of the two line image sensors to be mixed. The filter separation scheme has the drawback that since the light components separated by the dichroic mirror or prism are propagated at an angle of 90 degrees to each other, the arrangement intervening between the imaging device and the image sensors is disproportionately complicated.